The present invention generally relates to an end face light-emitting element having an increased light emission efficiency and a self-scanning light-emitting element array using such end face light-emitting elements, particularly to a three-terminal end face light-emitting thyristor and a self-scanning light-emitting element array using such three-terminal end face light-emitting thyristors.
An end face light-emitting diode array has heretofore been known as a high-density light-emitting element array which may increase a coupling efficiency to lenses. The basic structure of such end face light-emitting diode arrays is described in xe2x80x9cIEEE Trans. Electron Devices, ED-26, 1230 (1979)xe2x80x9d, for example. Conventional end face light-emitting diode arrays, however, have problems such that there are difficulties in fabricating them high-density, compact and low-cost, because each of diodes is to be connected to a driving circuit in order to drive the end face light-emitting diode array.
To resolve these problems, the present applicant has already disclosed a self-scanning end face light-emitting element array having a pnpn structure in which a driving circuit and a light-emitting element array are integrated in one chip (see Japanese Patent Publication No. 9-85985). A three-terminal end face light-emitting thyristor which is used as the end face light-emitting element disclosed in this publication is shown in FIGS. 1A and 1B. FIG. 1A shows plan view and FIG. 1B cross-sectional view taken along the X-Y line in FIG. 1A.
The end face light-emitting thyristor comprises an n-type semiconductor layer 12, a p-type semiconductor layer 14, an n-type semiconductor layer 16, and a p-type semiconductor layer 18 formed on an n-type semiconductor substrate 10; an anode electrode 20 formed on the p-type semiconductor 18 so as to make ohmic contact therewith; and a gate electrode 22 formed on the n-type semiconductor layer 16 so as to make ohmic contact therewith. On the entire structure provided is an insulting film (not shown) made of a light-transmitting, insulating material, on which an Al wiring 24 is further provided (see FIG. 1A). The Al wiring 24 is not shown in FIG. 1B for simplifying the figure. In the insulating film opened is a contact hole 26 for electrically connecting the anode electrode 20 to the Al wiring 26. While not shown in FIG. 1B, a cathode electrode is provided on the bottom surface of the substrate 10.
In this conventional end face light-emitting thyristor, light is emitted from an end face 23 of the semiconductor layers 14, 16 both thereof constitute gate layers. As shown by arrows in FIG. 1B, the most of current fed from the anode electrode 20 flows directly downward (this injected current is indicated by I1), and a part of the current flows going round to the gate electrode 22 (this injected current is indicated by I2). Although both of these injected current I1 and I2 contribute to light generation in the semiconductor layers, the light generated by the current I2 cannot contribute to external light emission from the end face 23 since the current I2 generates light in the area apart from the end face 23. As a result, the amount of light emitted from the end face is reduced only by the amount of light not contributed, thus external light emission efficiency is decreased.
An object of the present invention is to provide an end face light-emitting thyristor having improved external light emission efficiency.
Another object of the present invention is to provide a self-scanning light-emitting element array using such end face light-emitting thyristor.
According to a first aspect of the present invention, an end face light-emitting thyristor for emitting light from an end face thereof comprises a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, a third semiconductor layer of the first conductivity type, and a fourth semiconductor layer of the second conductivity type stacked in that order on a substrate of the first conductivity type; an electrode provided in such a manner that a part thereof makes ohmic contact with the fourth semiconductor layer in the vicinity of the end face for injecting current into the semiconductor layers; and an insulating layer provided between the fourth semiconductor layer and the part of the electrode that is not made ohmic contact with the fourth semiconductor layer.
It is also possible that an opening is formed in the part of the insulating layer faced to the end face, making the electrode ohmic contact with the fourth semiconductor layer via the opening.
In this way, the flow of the current injected from the electrode is concentrated to near the end face of the light-emitting thyristor.
According to a second aspect of the present invention, an end face light-emitting thyristor for emitting light from an end face thereof comprises a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, a third semiconductor layer of the first conductivity type, and a fourth semiconductor layer of the second conductivity type stacked in that order on a substrate of the first conductivity type; a first electrode provided on the fourth semiconductor layer; and a second electrode provided on the third semiconductor layer. The first, second and third semiconductor layers have a necked portion or a groove between a region including the first electrode and a region including the second electrode.
By providing such necked portion or groove, the resistance value between the region including the first electrode and the region including the second electrode becomes larger. As a result, the external emission efficiency is increased because the current component which flows toward the region including the second electrode is decreased, thus the most of the injected current flows in the region including the first electrode.
Using end face light-emitting thyristor described above, a self-scanning light-emitting element array of the following structure may be implemented.
A first structure of the self-scanning light-emitting element array comprises a plurality of light-emitting elements each having a control electrode for controlling threshold voltage or current for light-emitting operation. The control electrodes of the light-emitting elements are connected to the control electrode of at least one light-emitting element located in the vicinity thereof via an interactive resistor or an electrically unidirectional element, and a plurality of wiring to which voltage or current is applied are connected to electrodes for controlling the light emission of light-emitting elements.
A second structure of the self-scanning light-emitting element array comprises a self-scanning transfer element array having such a structure that a plurality of transfer elements each having a control electrode for controlling threshold voltage or current for transfer operation are arranged, the control electrodes of the transfer elements are connected to the control electrode of at least one transfer element located in the vicinity thereof via an interactive resistor or an electrically unidirectional element, power-supply lines are connected to the transfer elements by electrical means, and clock lines are connected to the transfer elements; and a light-emitting element array having such a structure that a plurality of light-emitting elements each having a control electrode for controlling threshold voltage or current are arranged, the control electrodes of the light-emitting element array are connected to the control electrodes of said transfer elements by electrical means, and lines for applying current for light emission of the light-emitting element are provided.
According to the structures described above, increased external emission efficiency, high-densitiy, compact and low-cost self-scanning light-emitting element arrays may be implemented.